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Existing electronic markets are fragmented in the sense that each is an information island. The interoperation of product information between them is difficult especially in semantics communication. This prevents the formation of global electronic markets and the lowering distribution cost through market globalisation. The traditional and contemporary ap-proaches of product standardisation and ontology mediation could solve the problem only if all markets could adopt the same product standards, or mediation systems could mediate all heterogeneous standards and markets without semantic conflicts. However, problems generally exist in adopting a universal standard or mediating all markets through existing mediation systems. A reflection of the issue is that there are millions of ad hoc electronic product catalogues (EPCs) situated in small and medium sized enterprises (SMEs), where each EPC is a semantic community, often not aware of standards and mediation systems due to its ad hoc nature. This thesis focuses on the semantic integration of autonomous ad hoc EPCs, which are semantically inconsistent with each other. Firstly, a novel Collaborative Concept Exchange (CONEX) approach is developed for the se-mantic integration of ad hoc EPCs. Using this approach, a PRODUCT MAP is first built based on the theories of semiotic analysis and market segmentation. It functions as an analytical framework to articulate ad hoc EPCs, and answers the questions: what are the general char-acteristics of ad hoc EPCs, what are their heterogeneous relations, and how they are unevenly distributed in fragmented electronic markets. Within this framework, an abstract representa-tion of ad hoc EPCs is proposed using the articulated elements that are simple and manipu-lable. Major contributions of this framework include: the models of the abstract representa-tion of ad hoc EPCs on their structures, concepts and contexts; the semantic integration conditions of heterogeneous ad hoc EPCs; and a ConexNet of market network topology that captures the characteristics of ad hoc EPCs that are unevenly distributed in fragmented elec-tronic markets. Secondly, a three-layer CONEX information model is proposed to integrate ad hoc EPCs based on the PRODUCT MAP, which provides a trichotomy of systems, designers and users. The strategy behind the model is the separation of structure from concept and context, and hence they can be independently managed to resolve semantic conflicts between ad hoc EPCs. The major contributions of this model include the CONEX framework, collaboration mechanism and context transformation. The CONEX framework presents a formal characteri-sation and reconstruction of the structures of ad hoc EPCs based on a CONEX structure model and a CONEX grammar. It provides a formal specification for representing ad hoc EPCs including concept structure, classifier structure and mapping structure. The semantic conflicts in designing the concepts of ad hoc EPCs are resolved by a collaboration mecha-nism based on a semantic consistency model. The collaboration mechanism includes three key procedures: replicating unique concept identifiers and translating concept definitions be-tween common concepts of common EPCs; localising common concepts to local EPCs; and globalising local concepts to common EPCs. Users in the CONEX information model are not involved in any integration activities. They are provided with automatic and accurate concept exchange services through a mechanism of context transformation, which is designed based on an algorithm called Heterogeneous Concept Transformation. The separate integration of structures, concepts and contexts of ad hoc EPCs guarantees that the requirements of flexi-bility, evolvability and exactness of semantic integration have been met. Thirdly, the feasibility and features of the Collaborative Concept Exchange approach have been demonstrated in a prototype implementation that provides the services of collaborative concept design for semantic conflict resolution, and heterogeneous concept transformation for accurate and automatic concept exchange between ad hoc EPCs. A key contribution in the implementation level is the independent representation of the CONEX framework called XML PRODUCT MAP (XPM). XPM provides a feature of platform independence by con-forming to the standards of W3C XML, Simple Object Access Protocol and Web Services Description Language in both document specification and document transport. It is also a demonstration that the generic CONEX structure model and CONEX grammar can be imple-mented in any specific language such as XML for the particular scenarios of semantic integra-tion. With the aid of a collection of XPM document templates, two components called Con-cept Collaborator and Concept Transformer of the CONEX prototype are implemented to demonstrate how concepts are collaboratively designed to resolve semantic conflicts and how concepts are automatically and accurately exchanged between autonomous, heterogeneous and distributed ad hoc EPCs.